iOS url出现特殊字符处理 -- stringByAddingPercentEncodingWithAllowedCharacters

stringbyaddingpercentescapesusingencoding(只对 `#%^{}[]|\"<> 加空格共14个字符编码，不包括”&?”等符号), ios9将淘汰，建议用 stringbyaddingpercentencodingwithallowedcharacters 方法

stringbyaddingpercentencodingwithallowedcharacters  需要传一个  nscharacterset  对象（关于  nscharacterset  文章说的很好）

如[nscharacterset  urlqueryallowedcharacterset]

urlfragmentallowedcharacterset  "#%<>[\]^`{|}

urlhostallowedcharacterset      "#%/<>?@\^`{|}

urlpasswordallowedcharacterset  "#%/:<>?@[\]^`{|}

urlpathallowedcharacterset      "#%;<>?[\]^`{|}

urlqueryallowedcharacterset    "#%<>[\]^`{|}

urluserallowedcharacterset      "#%/:<>?@[\]^`

（2）网络访问请求：中文空格字符解码

stringbyremovingpercentencoding  ----  xcode7可能会提示要将stringbyaddingpercentescapesusingencoding替换成此方法，要根据是否是解码来区分

代替  stringbyaddingpercentescapesusingencoding

let customallowedset =  nscharacterset(charactersinstring:"`#%^{}\"[]|\\<> ").invertedset

nsstring *urlstr = [urlstr stringbyaddingpercentencodingwithallowedcharacters:[[nscharacterset charactersetwithcharactersinstring:@"?!@#$^&%*+,:;='\"`<>()[]{}/\\| "] invertedset]];